1. Technical Field
The present application relates generally to an improved data processing system and method. More specifically, the present application is directed to a system and method for thresholding system power loss notifications in a data processing system.
2. Description of Related Art
As with most data processing devices in today's 24 hour a day, seven day a week world, modern storage systems are vulnerable to Power (or Pulse) Line Disturbance (PLD) events, e.g., power utility grid interruptions, such as may be due to lightning strikes or the like. A PLD is a transient or temporary fluctuation in power supplied over a power line to an electronic device. While a PLD may cause a fluctuation in the power provided to a data processing device, in general, the PLD is a recoverable event, i.e. it is not a power loss event that requires the shutting down of the data processing system.
Some locales experience frequent PLD event conditions during “stormy” times. However, it is undesirable to shutdown a data processing system, such as a storage system, for example, because of such frequent PLD events since the data processing system may easily recover from PLD events. If a storage system is shut down, for example, data availability is lost and there may be potential data integrity issues for I/O operations that may be pending. Thus, it is imperative that storage systems and other data processing systems be able to weather PLD events.
Besides the issue of PLDs, storage systems and other data processing systems must also be concerned about more permanent power outages, such as loss of all AC line cord power. Such AC loss events need to be properly handled by having power systems that support an Early Power Off Warning (EPOW) function. This function is used to properly and orderly quiesce input/output (I/O) activity to the storage devices of a storage system or data processing system prior to the power decay being seen by the storage devices. Writing data to a storage device, such as a disk drive, while its power is decaying can result in data integrity problems.
Moreover, storage systems that support write caching, i.e. sending an acknowledgement to an initiator of the write operation indicating completion of the write operation prior to the actual data being made persistent on storage media, are required to provide a guarantee that the data will be retrievable even if there is a power outage. Thus, both PLD and EPOW events must be handled by storage systems and other data processing systems.
It should be appreciated that “real” EPOW events are effectively permanent PLDs which cause all power to be lost to the system. To accommodate real EPOW events and temporary PLD events, a system typically must include costly and complex power supply system mechanisms for implementing a sufficient holdup capacitance time to accommodate a reasonably long PLD event, as well as continued holdup capacitance time to support quiescing storage device activity prior to the actual voltage boundaries decaying, i.e. becoming out of specification. This is generally achieved with the power supply output capacitance. In order to achieve desired PLD ride through and EPOW time, i.e. holdup capacitance time, some systems implement power supplies with large amounts of added capacitance or other power extending technology, e.g., super capacitors, batteries, etc., to the power supply system implementation.
It should be appreciated that the additional capacitance added to systems, to provide some level of power holdup capacitance time, increases the cost and complexity of the overall system. Because of this cost and complexity, some products choose to not implement such extensive mechanisms. In fact, standard practice for conventional power supply system design uses a single mechanism for indicating a PLD event or a “real” EPOW event. That is, when a PLD event occurs the power system also generates an EPOW event, just as with the “real” power loss case, which results in the same system behavior as the “real” EPOW event. In other words, PLD events are mapped into EPOW events and thus, are handled in the same fashion. This creates a problem whereby the system may not be able to differentiate between a real EPOW event and a PLD event.